Conventional Drying Research Articles

Low-Temperature Rapid Drying of Viscous Sludge Via Non-Phase Change Based on Particle High-Speed Self-Rotation and Medium Dispersion in Cyclone

Drying operations are of grave importance to realize the reduction and utilization of sewage sludge resources, but the conventional thermal evaporation drying (TED) technology faces challenges due to the need for a large amount of thermal energy to conquer the phase-change latent heat of moisture. Herein, we report a non-phase change technology based on particle high-speed self-rotation in a cyclone for fast, low-temperature drying of viscous sludge with high moisture contents. Dispersed phase medium (DPM) is introduced into the cyclone self-rotation drying (CSRD) reactor to enhance the dispersion of the viscous sludge. The effects of carrier gas temperature, feeding rate, size, and proportion of DPM particles in the drying process are systematically examined. Under optimal operating conditions, the weighted content of moisture in the viscous sludge could be reduced from 80% to 15.01% in less than 5 s, achieving a high drying efficiency of 95.79%. Theoretical calculations also reveal that 89.26% of the moisture is removed through a phase change pathway, contributing to a 522-fold increase in the drying rate of CSRD compared to TED technology. This investigation presents a sustainable effective approach for high moisture viscous sludge treatment with low energy consumption and carbon emissions.

Performance investigation of newly developed novel hemispherical solar dryer for sustainable food preservation: Comparative analysis with traditional methods

To preserve the world’s food resources, drying agricultural products is crucial for prolonging their shelf life. A novel concept of 1.5 m hemispherical solar dryer surmounts the limitations of conventional dryers like long drying time, solar tracking, large space requirement etc. Trials were performed on Thomson grapes to convert into raisins. For the purpose of fair accuracy in comparison, experiments were conducted on hemispherical solar dryer (active and passive mode), traditional cabinet solar dryer as well as open sun drying (OSD) by maintaining the uniform test conditions. An average moisture removal rate of 0.1935096 kg/h was obtained in hemispherical dryer. The hemispherical solar dryer significantly reduced drying time for converging grapes into raisins to 13 days, compared to 18 days in a cabinet solar dryer and 19 days with OSD. The hemispherical dryer, through a gap, creates a greenhouse effect, reaching a 70.1 °C maximum temperature and an average of 60.7 °C at 796 W/m2 average solar energy. The hemispherical dryer attained a drying efficiency of 5.67 %. Six mathematical models were employed for hemispherical and cabinet dryers. Amongst these Two term and Wang & Singh models were found suitable for the experimental data and provided precise prediction of moisture ratio.

The significance of biowaste drying analysis as a key pre-treatment for transforming it into a sustainable biomass feedstock.

The objective of this study is to investigate the drying kinetics of fruit and vegetable peel biowaste using a sustainable technique as a key-pretreatment for its conversion into useful feedstock. Biowaste represents a missed potential source of bioenergy and bioproducts, but moisture removal is required, and conventional drying methods are expensive since they require great quantity of energy supplied, almost always, by a non-renewable energy. In this study six batches with the same quantity of biowaste, and heterogeneous physical composition were dried under open-sun conditions. We evaluated the influence of the interaction between drying area and the initial moisture content on drying rate. Eight semi-theoretical models were fitted using Levenberg-Marquardt algorithm to predict drying rate, and their accuracy was assessed through goodness-of-fit tests. Maximum moisture content to preserve biomass (10%) was reached on 5th day and the equilibrium on 16th day of drying. According to goodness-of-fit test (R 2=0.999, χ 2=4.666×10-5, RMSE = 0.00683) the best model to predict drying rate was Two-term model. The mathematical model obtained from Fick's second law is reliable to predict drying kinetics, R2 (0.9648±0.0106); despite the variation between drying area and initial moisture content. Kruskal-Wallis test showed that drying rates between batches are not significantly different (p=0.639; 0.05); nor effective diffusion coefficient (D eff =4.97×10-11±0.3491×10-11), (p=0.723; 0.05). The study of drying kinetics is crucial for selecting the optimal biowaste treatment based on its generation context. This could enable its use as feedstock for bioproduct or bioenergy production, thereby reducing waste accumulation in landfills and environmental impact.

Potential Utilisation of Solar-Assisted Kiln Dryer in Bamboo Drying

Bamboo is increasingly used as an alternative material for producing renewable and environmentally friendly products. Bamboo should be dried before use to increase its stability and improve its resistance against biodeterioration agents. The most common drying method for bamboo is through air-drying. Alternatively, artificial drying, such as solar drying, can produce optimum drying results regarding the drying rate and quality of bamboo throughput. This study investigated the potential utilisation of solar drying methods for processing local bamboo. The drying characteristics and physical and mechanical properties of solar-dried Gigantochloa levis bamboo culms’ bottom, middle, and top sections were determined. The drying time of G. levis culm has been reduced to about 40 days compared to the conventional air drying of 70 days using the solar-assisted kiln dryer. Solar-dried culms have a lower final moisture content of 20% than air-dried ones. The average circumference and diameter shrinkage values of solar-dried G. levis culms from green to approximately 12% moisture content were 3.22% and 4.29%, respectively, and the wall thickness shrinkage was 8.12%. The mean values of modulus of rupture and modulus of elasticity of solar-dried G. levis culm were 63.75 and 12567.99 N mm-2, respectively, while its mean values of compression and shear parallel to fibre were 45.87 and 10.01 N mm-2, respectively. The quality of solar-dried G. levis culms produced in this study showed the viability of using a solar-assisted kiln-dryer as a potential alternative processing method for drying local bamboo species in Malaysia.

Social life cycle sustainability assessment of dried tomato products based on material and process selection through multi-criteria decision making.

Tomatoes are a significant product of the Mediterranean region and a crucial component of the Mediterranean diet. The formulation of dried tomato products enriched with proteins and bioactive compounds could be a strategic approach to promote adherence to the Mediterranean diet. Six different novel tomato products were analyzed using different protein enrichment sources (pea proteins and leaf proteins) and drying technologies (hot-air dryer, microwave vacuum dryer, and conventional dryer). The novelty of this approach lies in combining product-specific criteria with global societal factors across their life cycles. Using 21 criteria and an analytic hierarchy process (AHP) survey of experts, the social sustainability score for each product was determined through a multi-criteria assessment. The tomato product's life cycles have minimal regional impacts on unemployment, access to drinking water, sanitation, or excessive working hours. However, they affect discrimination, migrant labor, children's education, and access to hospital beds significantly. The study identified nutritional quality as the top criterion, with the most sustainable design being a tomato bar enriched with pea protein and processed using microwave vacuum drying. The study revealed that integrating sensory and nutrient compounds into social sustainability assessments improves food sustainability and provides a practical roadmap for social life cycle assessments of food products. It emphasized the importance of considering global social issues when reformulating Mediterranean products to ensure long-term adherence to the Mediterranean diet. Incorporating social factors into sustainability scores can also enhance the effectiveness of product information for conscious customers. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Comparative study on the difference of saponins and nutrients in Panax notoginseng powder dried by new rapid drying technique and traditional hot air.

Panax notoginseng (Burk.) F. H. Chen (PN), commonly known as PN, is a nutritious natural food with a long history of consumption and has traditionally been used for dietary purposes in the form of dried processed products. Currently, developed a dry processing at short time and room temperature (DRST), which is characterized by high efficiency and low cost. However, there are few studies on the impact of DSRT. In this study, the effects of conventional hot air drying (DHA) and the innovative drying technology DSRT on the key components of PN were evaluated for the first time. The results showed that DRST could obtain processed PN products with smaller particle sizes and that DRST-treated PN could increase the content of five saponins by 1.38% for Ginsenoside Rg1, 0.1% for Ginsenoside Re, 0.83% for Ginsenoside Rb1, 0.16% for Ginsenoside Rd, and 0.36% for PN saponin R1, relative to the content of five saponins that could be increased by conventional DHA. The metabolome results yielded a total of 1401 metabolites identified and analyzed, and 201 metabolites showed significant differences between the two techniques, which were expressed as amino acids, flavonoids, and other nutrient-active components. The results of this study indicate that the PN products produced by DRST technology have higher nutritional quality compared to traditional processing. This study provides support in the processing of PN and the development of PN products.

Non-hydrolytic sol-gel synthesis of amine-functionalized silica: Template- and catalyst-free preparation of mesoporous catalysts for CO2 valorization

Carbon dioxide utilization presents an important and topical research topic. However, the performance of catalysts needed for CO2 transformations does not achieve the necessary levels for their widespread application. To this end, we decided to study non-aqueous condensations providing amine-functionalized silica catalysts, possibly active in CO2-epoxide cycloaddition reaction. While non-hydrolytic sol-gel method is well-known for its efficiency in providing highly porous Lewis and Brønsted acid metallosilicates, here we show for the first time its application for the preparation of silica-based catalysts containing basic groups. First, the reaction conditions were screened to reproducibly obtain porous materials with preserved amine moieties. These were identified as follows: silicon tetraacetate and bridging tertiary amine silanes as precursors, toluene as a solvent, and temperature between 160 and 180 °C. In such a way, materials with up to 776 m2 g−1 and 1.58 cm3 g−1 were obtained in one-step process, without any template, after conventional drying step. Next, the amine-functionalized materials were tested in CO2-epoxide coupling providing cyclic organic carbonates with high selectivity (>99 %) and moderate activity (up to 86 % epichlorohydrin conversion after 1 h at 120 °C and 10 bar CO2). The characterization of spent catalysts revealed a presence of cyclic organic carbonates at the catalyst surface as well as conversion of tertiary amine groups to quaternary ammonium moieties.

Influence of drying method on the shelf life of artisanal pasta

Efforts to optimize pasta drying often face challenges due to the complexity of operational variables. This study aimed to optimize conventional fixed-bed convective drying of artisanal pasta using a desirability function approach and assess the influence of drying methods on shelf life. Three methods were compared: optimized conventional fixed-bed convective drying (O-CFBCD), hot air microwave drying (HAMD), and convective tray drying (CTD). This study underscores the importance of exploring and regulating pasta quality parameters to meet both industry standards and consumer preferences for marketable products with sensory appeal. While all three drying methods show promise for producing quality pasta, there is a need for improved initial moisture control, particularly in the CTD condition, to ensure compliance with regulatory standards and mitigate microbiological risks associated with high water content. Over time, most sensory parameters exhibited enhancement, aligning with consumer expectations for high-quality products. This suggests that continuous monitoring and optimization of drying processes are essential for maintaining and improving pasta quality throughout its shelf life.

Comparison of energy consumption and probiotic stability with pilot scale drying processes

The production of dried probiotics offers multiple advantages including expanded storage options, ease of transportation, enhanced stability, formulation support, and incorporation into a variety of finished products. As probiotic use and application areas increase, the demand for lower production costs and increased product stability follows. The most common methods for drying include lyophilization and spray drying. Lyophilization offers high preservation of viability at the expense of production speed, while spray drying provides high throughput drying with greater loss of probiotic viability. Newer processes, such as electrostatic spray drying, have the potential to bridge the gap. The aim of this study was to evaluate the energy consumption and viability of Lacticaseibacillus rhamnosus GG (LGG) with pilot-scale conventional spray drying, electrostatic spray drying, and lyophilization. Energy consumption of the primary utilities was monitored along with LGG viability immediately and 8-12 weeks after drying. With regards to removal of water, conventional spray drying was the most energy efficient (1.2 kWh/L), followed by electrostatic spray drying (10.9 kWh/L) and lyophilization (16.9 kWh/L). When normalized against recovered viable LGG, electrostatic spray drying was the most efficient at 4.6x1010 CFU/kWh, followed by lyophilization and conventional spray drying at 1.1x1010 CFU/kWh and 4.8x107 CFU/kWh, respectively.

Simultaneous use of convection and radiation heat transfer for Iranian pistachio drying using catalytic heater - numerical and experimental study

This study presents a comprehensive investigation into the simultaneous use of convection and radiation heat transfer for Iranian pistachio drying using a catalytic heater. Both experimental and numerical analyses were conducted to evaluate the performance of the proposed system. The experimental setup involved a catalytic infrared heater, which provided a consistent temperature of approximately 370 K within the drying chamber. The results indicated that the drying time was reduced by 40% compared to traditional hot air drying methods, with an average moisture reduction rate of 0.8% per minute. The numerical analysis, conducted using computational fluid dynamics (CFD) simulations, supported the experimental findings, showing a uniform temperature distribution across the pistachios and efficient heat transfer. The catalytic heater demonstrated a combustion efficiency of 98%, with CO emissions below 10 ppm and zero NOx emissions, highlighting its environmental benefits. Overall, the combined experimental and numerical results confirmed that the proposed catalytic heater system not only enhances drying efficiency but also significantly reduces energy consumption and greenhouse gas emissions compared to conventional drying methods.

Monitoring and Information System for Automatic Clothes Drying Based on the Internet of Things

This research develops an Internet of Things (IoT)-based automatic clothes drying monitoring and information system to overcome the challenges of drying clothes due to uncertain weather changes. The system integrates NodeMCU ESP8266 as the main controller with various sensors such as rain, light, temperature, and humidity sensors to detect environmental conditions. The servo motor is used as a driving force to move the clothesline. The smartphone-based user interface was developed using the MIT App Inventor to enable remote monitoring and control. The test results showed that the system successfully detected weather changes and responded automatically, providing real-time information to users. Implementing IoT technology in this system allows for more efficient and practical management of clotheslines, overcoming the limitations of conventional drying methods.

Drying Hot Red Chilies: A Comparative Study of Solar-Gas-Fired, Tunnel, and Conventional Dryers

Drying Hot Red Chilies: A Comparative Study of Solar-Gas-Fired, Tunnel, and Conventional Dryers

Kinetic study and modelling of drying of Chlorellavulgaris

Microalgae, a versatile source of biofuels, chemicals, and nutraceuticals, necessitates efficient drying for subsequent applications. Extensive studies have been done on the benefits and uses of microalgae, but very few are focusing on drying. This research focused on a specific microalga, Chlorella vulgaris, to analyze the drying kinetics involved in the moisture removal process. Data on drying behavior were collected using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). As the temperature rose, the moisture content of the biomass rapidly decreased and peaked between 65 and 80 °C. From four widely used drying kinetics models, which are typically used to analyze the drying kinetics of agricultural goods, four non-isothermal drying models were derived. These models were assessed using the coefficient of determination (R2) and reduced chi-square (χ2). Page's model emerged as the best fit for describing drying kinetics. This study introduces a novel approach to characterize the intrinsic properties of freshly harvested Chlorella vulgaris by employing TGA and DSC. Unlike other studies focusing on conventional drying methods, our investigation provides real-time insights into the microalgae's thermal behavior during drying.

Innovation in Cassava Bagasse Valorization: Efficiency of Convective Drying Enhanced with Ultrasound and Pulsed Electric Fields.

This research proposes an efficient alternative for dehydrating cassava bagasse to address the inherent challenges in the handling, transportation, storage, and preservation of this agro-industrial residue generated in cassava starch production plants. This residue is characterized by high moisture retention, considerable volume, and hydrophilic nature, complicating conventional drying methods. This study evaluates the impact of emerging ultrasound (US) and pulsed electric field (PEF) technologies prior to convective drying to enhance the dehydration efficiency of cassava bagasse, aiming at its valorization and contributing to the sustainability of the cassava starch industry. The findings reveal that pretreatment with ultrasound (US) and pulsed electric fields (PEF) significantly reduces the drying time of cassava bagasse compared to convective drying alone. With probe ultrasound at 26 kHz for 30 min, the drying time is reduced by 72% (3.83 h vs. 14.0 h); with bath ultrasound at 37 kHz for 30 min, it is reduced by 56.0% (6.16 h vs. 14.0 h); and with PEF at 7.5 kV/cm for 30 min, it is reduced by 52.4% (6.66 h vs. 14.0 h). These emerging technologies increased the effective diffusivity and modified the molecular structure of the bagasse, thereby improving mass transfer and drying process efficiency. These results are particularly useful for developing more efficient and sustainable strategies for drying agricultural by-products, with direct implications for the post-industrial treatment of agro-industrial residues with high water content.

Energy Performance of Zeolite-Based Drying Bead Desiccants Used to Dry Paddy Rice.

This study utilizes differential scanning calorimetry and thermogravimetric analysis to assess the total energy required to regenerate saturated zeolite-based drying beads (DBs) used to dry paddy rice. We quantify the required heat energy for DB regeneration by calculating the area under the curve in a heat flow rate versus time graph, with the end of the regeneration process indicated by stabilization of the DB weight. Our findings suggest that at DB regeneration temperatures ranging from 120 to 350 °C, the process varied from 813 to 22 min, demonstrating that higher temperatures lead to faster regeneration speeds. The total energy used for regeneration showed similar values at 250 and 350 °C, averaging around 2032 and 2136 kJ per kg of dried DB, respectively. Additionally, the study showed that DBs can hold water between 28.7% and 54.4% higher than the manufacturer's specifications, suggesting a reduced quantity of DBs required for effective paddy rice drying. The overall required heat energy for the regeneration process was calculated at 4.86 MJ/kg, with a carbon intensity of approximately 275.61 g of CO2-eq per kg of water removed, resulting in lower values compared to conventional drying methods. The study underscores DB's possibility of lower total energy (thermal and electrical) consumption and greenhouse gas emissions, alongside its flexibility to regenerate with intermittent energy sources.

Effect of freeze-thaw and PEF pretreatments on the kinetics and microstructure of convective and ultrasound-assisted drying of orange peel

The main waste generated by juice industry comprises orange peels, which have a great upcycling potential once stabilized. Drying is the most used method for this purpose, but the high energy consumption prompts interest in its intensification. This study assessed the influence of freeze-thaw and pulsed electric field (PEF) pretreatments in conventional and airborne ultrasound-assisted drying (50 °C) of orange peels. None of these pretreatments alone got to reduce processing times significantly, but combined with ultrasound-assisted drying produced a significant shortening of the process. This was particularly important in the lower intensity PEF pretreatment tested (0.33 kJ/kg), indicating the existence of optimum conditions to carry out the pretreatments. Microstructure analysis revealed that the application of ultrasound during drying led to better preservation of the sample structure. Thus, the integration of pretreatment techniques to ultrasound-assisted drying may not only shorten the process but also help to preserve the original structure.

Evaluating the feasibility of powder milk production by pulse spray drying: An approach on sensory properties, toxicological assessment, and microbial inactivation

The potential of a new spray drying technology (pulse spray drying, PSD) was explored in drying milk, using two outlet temperatures. Sensory attributes, instrumental color properties, and volatile compounds were examined. Additionally, the effect of PSD on the food's chemical safety was measured by CALUX® bioassays. For these approaches, milk was also dried by conventional spray drying (SD) and lyophilization (LYO). Finally, the impact of PSD on the microbiological load was investigated using Pediococcus acidilactici ATCC 8042, as a non-pathogenic surrogate of enteric pathogens. In sensory analysis, reconstituted PSD samples were scored with higher color, odor, and flavor intensities than LYO and SD. Volatiles like γ-hexalactone, acetic acid, and ethyl acetate could have contributed to these particularities. Accordingly, instrumental color revealed differences between the four treatments, showing a more evident yellowish coloration and higher saturation in PSD milk. Cytotox, PXR, and p53 CALUX® results in PSD samples ranged from 0.11 to 0.21 μg Tributyltin acetate eq./g, 0.30–0.51 μg Nicardipine eq./g, and were under quantification limit, respectively. These findings indicated that PSD does not pose an increased toxicological risk compared to other drying technologies. Viability results of Pediococcus acidilactici during PSD showed that the higher the outlet temperature, the lower the cell viability. In conclusion, all data raised in this study evidenced that PSD could be used in milk drying without compromising its quality and safety. Industrial relevanceConsidering the low energetic consumption described in several works, pulse spray drying could be a promising approach for the food sector. In addition, it may play a relevant role in overcoming the limitations of conventional spray dryers in terms of viscosity. The results obtained in this study are one of the first in this field and show the feasibility of milk powder production without compromising its quality and safety.

Organic acid preservation of cereal grains improves grain quality, growth performance, and intestinal health of post-weaned pigs

This study investigated the effect of preserving wheat and barley grains with an organic acid liquid surfactant mould inhibitor compared to conventional artificial drying and assessed its effects on the health and performance of pigs post-weaning (PW). A 2 × 2 factorial arrangement was conducted to investigate the interaction between grain preservation method (dried vs. preserved) and zinc oxide (ZnO) inclusion (yes vs. no) on growth performance, diarrhoea scores and incidence, and total tract nutrient digestibility. One hundred and ninety-two pigs (3 pigs/pen; 16 replicates/treatment) were assigned to one of four experimental diets for 35 days: (1) dried grain diet, (2) preserved grain diet, (3) dried grain diet with ZnO and (4) preserved grain diet with ZnO. Diets were formulated to contain similar levels of net energy and standardised ileal digestible lysine. On day 35 PW, 24 pigs (12 replicates/treatment) from the non-ZnO supplemented groups were euthanised and digesta was collected for coefficient of apparent ileal digestibility (CAID), gut microbial population and volatile fatty acid analysis. Stomach tissue was also collected for gene expression analysis, as well as small intestine samples for gut morphology. Notable improvements in grain quality were observed in the preserved grain, including a reduction in grain pH, mould presence, and contamination by mycotoxins, specifically deoxynivalenol in wheat and barley, and ochratoxin A and HT-2 toxin in barley. The preserved grain diet improved average daily gain (ADG; P < 0.01) and body weight (BW; P < 0.01) compared to the dried grain diet. The incorporation of ZnO increased average daily feed intake (ADFI; P < 0.01) and BW (P < 0.05) in the dried grain diet, however, ZnO did not affect ADFI (P > 0.05), and reduced ADG and BW in the preserved grain diet (P < 0.05). Pigs offered the preserved grain diet had reduced faecal scores and diarrhoea incidence compared to those offered the dried grain diet (P < 0.05). Supplementation of ZnO reduced faecal scores and diarrhoea incidence compared to non-supplemented pigs (P < 0.001). On day 35 PW, the preserved grain diet had improved CAID of nitrogen and gross energy (P < 0.05), lower levels of colonic branched-chain volatile fatty acids (P < 0.05), and beneficial shifts in gut microbial populations. Specifically, there was a reduction in ileal Streptococcus (P < 0.001) and an increased abundance of colonic Faecalibacterium (P < 0.05). In conclusion, organic acid preservation improved grain quality, benefiting post-weaned pigs through improved nutrient digestibility and gut health, thus enhancing overall growth performance PW.

Spherical nanocrystalline ScYSZ thermal barrier material by a novel supersonic plasma spheroidization method: Simple synthesis and excellent performance

The performance of plasma sprayed thermal barrier coatings (TBCs) is strongly dependent on the quality of the feedstock powders, which usually are fabricated by conventional spray drying and multi-step sintering methods. In this work, a novel supersonic plasma spheroidization technology was employed to fabricate the spherical nanocrystalline Sc2O3-Y2O3 co-stabilized ZrO2 (ScYSZ) powder. The deformation process from the irregular powder to the spherical one was stimulated by the COMSOL phase field simulation. The results suggested that the original irregular pyrolysis products of ScYSZ precursors were aggregated into spherical powders by plasma spheroidization technology. The COMSOL simulations verified that the powder changed from irregular particles to spherical ones. The spheroidized ScYSZ particles exclusively consisted of non-transformed t’-ZrO2 phase and showed good fluidity, smooth surface and high apparent density, which were expected to have a broader application prospect in the field of TBCs and other ceramic coatings.

Experimental analysis of conductive drying of paper and board

The primary heat transfer source in the conventional multi-cylinder drying of paper and board is conduction. Conduction is facilitated by high-tension contact with steam-heated cylinders, while convective drying, the main mass transfer source, operates as heated air flows over the article web in the pockets. This conduction process occurs at elevated temperatures and contact pressures to ensure effective contact between the wet paper web and the heated cylinders. The contact pressures and temperatures of the hot surface significantly influence the conductive drying characteristics. This research paper presents an experimental study that involves designing a simple lab-scale setup with in-situ and continuous sensing capabilities for various commercially available grades of paper and board. Embedded thermocouples measure the temperatures of the heated platen and the sheet, allowing the collection of flux data to determine heat transfer characteristics. The goal of this study is to ascertain the instantaneous contact coefficients for different basis weights as a function of moisture content. The acquired data will provide valuable insights and information toward process development, design, and simulation of the article drying process.